1. Field of the Invention
The present invention relates to an inexpensive automatic intravenous flow control device.
2. Description of the prior Art
Devices are known for controlling the flow of intravenous (IV) fluids to a patient. For example, infusion pumps may be used to control the flow of IV fluids to a patient within 10-20% of the prescribed infusion rate. However, infusion pumps are bulky, expensive, and require periodic maintenance.
Simple clamps may be applied to the IV line and may provide acceptable flow control in certain non-critical circumstances. The desired IV drip rate is determined by adjusting the clamp at the beginning of the IV infusion, but must be checked regularly. Because drop size varies with the viscosity of the IV fluid, the drip rate required to give a predictable rate of infusion will vary from solution to solution. Also, changes in the height of the fluid level in the IV container relative to the patient (for example, when the patient sits up or gets out of bed or as the fluid level in the IV container falls) result in changes in the drip rate. This device may be inexpensive but it lacks safety and accuracy.
Variable resistance devices (e.g., Dial-A-Flow by Abbott Laboratories) may also be used as an integral part of the IV line. This device is also sensitive to viscosity changes and requires a constant hydrostatic pressure to maintain constant flow and therefore is subject to the same inaccuracies as the simple clamp discussed above. These devices can be recalibrated for solutions of known viscosity, but such a minor advantage probably fails to justify the increased expense of such devices for routine use.
Gravity-fed pressure-compensating devices (e.g., Isoflux by Geistlich) may also be used to control IV flow. This device has a flexible diaphragm that partially compensates for changes in hydrostatic and venous pressures. While the rate of infusion is more constant and therefore more accurate than the simple clamp, these devices are quite expensive.
Electronic gravity-fed controllers (e.g., Accudot by Imed) are flow control devices that use a variable resistor that is incorporated into the IV set and is adjusted automatically by an electronic controller. Because the controller monitors the drip rate, the infusion rate also varies from solution to solution. However, the rate of flow is not affected by changes in patient position or venous pressure. Again, while the infusion rate is relatively accurate, these controllers are quite expensive.
U.S. Pat. No. 4,361,147 discloses a flow control device for administering IV fluids wherein the fluid flow may be controlled by a spring-biased fluid control cam. Again, such a device is quite expensive to produce.
U.S. Pat. No. 4,324,239 discloses a safety valve for catheterization procedures wherein a piston having an internal flow path is biased by a resilient member such that as fluid pressure increases in the valve, fluid flow through valve also increases. Such a device would be unusable to provide a relatively constant fluid flow through an IV flow controller.
Thus, what is needed is an inexpensive, easy-to-manufacture, easy-to-use IV fluid flow controller that can provide accurate control of fluid flow into the patient. Such a device should be able to be incorporated as an integral part of the IV infusion set so as not to be easily removable.